Three main studies are being undertaken during the current project period. First, stop-flow techniques are being used to continue cataloguing the parameters of rapid axonal transport of specific substances of interest for their role in neurotransmission. Five such substances, including nonrepinephrine and all of the enzymes involved in its synthesis, have been studied by this means to date. Choline acetyltransferase and substance P will be examined next. Second, experiments are being continued on the localization and fate of acetylcholinesterase in peripheral nerve. Our recent observation that this enzyme is not only transported to nerve terminals but also is released from them in response to action potentials is being pursued. Studies will be carried out to determine if the release of enzyme is affected in the same way as the release of neurotransmitter in the presence of drugs such as vinblastine and black widow spider venom. A monospecific antiserum against acetylcholinesterase is being prepared as a tool for immunohistochemical studies of the localization and turnover of this enzyme. Third, studies are being continued to probe the kinetics of axonal transport. The hypothesis is being tested that microtubules determine the capacity of the transport system and that excess capacity is related to a surplus of microtubules. Further experiments are being performed to learn whether there are any nerves and conditions in which transport velocity is affected by changes in the amount of material in motion.